This invention relates to a method of on-line control of the opacity of a moving sheet material and, more particularly, to a method on-line control of the opacity of a film-fibril strand sheet material wherein the opacity of the sheet is a function of a thermal bonding finishing process applied to each side of the sheet.
U.S. Pat. No. 3,169,899 to Stueber describes the formation of film-fibril sheets by random overlapping deposition of continuous fibrillated strands. These strands described in Blades et al. U.S. Pat. No. 3,081,519 are each characterized as a three-dimensional network of film-fibrils which are interconnected at random intervals along and across the strand.
U.S. Pat. No. 3,442,740 to David describes a thermal bonding process and apparatus for film-fibril sheet material and recognizes the effect of heat treatment in a platen press upon opacity of film-fibril sheets.
U.S. Pat. No. 4,098,641 to Casey describes a method for on-line control of the opacity of paper which varies in basis weight wherein an opacity additive also varies basis weight as well as opacity.